The main objective of this research is to study the mechanism of food vacuole formation (phagocytosis) in Tetrahymena and its contribution to the general physiology of the cell. To accomplish this, we intend to perform a genetic dissection, that is, to study a collection of mutants which are individually defective in single different components of this interesting mechanism, characterize the defect in each mutant down to the molecular level if possible, and thereby characterize the normal mechanism in the wild-type strain. Our success at growing one such mutant without phagocytosis presents us with an experimental system which appears unique among animal cells. This system should be invaluable for a) dissecting out routes of uptake of various compounds; b) studying plasma membrane uptake without the intractable complication of phagocytic uptake; c) understanding the role of phagocytosis in other related cellular processes (e.g., synthesis of the digestive enzymes, excretion) and d) understanding how a complex cellular structure is assembled. Concepts and approaches developed in this study may find application in basic and clinical medicine, in view of the important roles played by phagocytosis in the immune response and in the clearing of particulate matter. This study may yield a better understanding of blood diseases and lung diseases traced to disorders of phagocytosis and to microparticle pollution. BIBLIOGRAPHIC REFERENCES: Orias, E. and L. Rasmussen. Dual capacity for nutrient uptake in Tetrahymena. IV. Growth without food vacuoles and its implications. Exp. Cell Res., in press, 1976. Orias, E. Ciliate Architecture: Derivation from a simple flagellate. Trans. Amer. Micro. Soc., 95: 419-433, in press, 1976.